Apparatus for locating reflecting surfaces and for measuring the curvatures thereof



amegol @n VA Aril 5, 1949.

H. S. EWING APPARATUS FOR LOCATING REFLECTING SURFACES AND FOR MEASURING'IHFg/CURVATURES THEREOF 3 Sheets-Sheet l 4Filed. Sept. 29, 1944 figApril `5, 1949.

H. S. EWING APPARATUS FOR LOCATING REFLECTING SURFACES AND FOR MEASURINGTHE GURYTURES THEREOF 3 Sheets-Sheet 2 Filed sept. 29, 1944 HERBERTELEM/INE,

g cfmwwm A1011l 5, 1949 H. s. EWING APPARATUS FOR LOCATING REELECTINGSURFACES AND FCR MESURING THE QURVTURES THEREOF Filed sept. 29, 1944 l 3Sheets-Sheet 3 HEREERT ELEM/m5,

Patented pr. 5, 1949 APPARATUS FOR LOCATING REFLECTING SURFACES AND FORMEASURING THE CURVATURES THEREOF Herbert S. Ewing, Philadelphia, Pa.Application September 29, 1944, Serial No. 556,436 s claims. (o1.zas-14) The invention described herein may be manufactured and used byor -for the Government y for governmental purposes, without the .paymentto me of any royalty thereon. g i

My invention relates to reflecting surfaces of optical and otherelements and it has special reference to means for locating suchsurfaces and for measuring the curvatures thereof. .h

Broadly stated, the object of my invention is to provide improvedapparatus by which the location and the curvature of surfaces of glass,metal or other material capable of reflecting light may readily bedetermined.

A more specific object is Ato facilitate accurate location of reflectingsurfaces having a wide variety of shapes and contours including flat,concave and convex.

Another `object is to facilitate curvature measurement of reflectingsurfaces having either concave or convex contour and being a part ofmirrors, optical lenses, metal balls, sections thereof, and otherelements of various shapes and materials.

Further objects are to increase the accuracy and reliability with whichsuch location and measurement may be effected; to simplify procedure ofthe named operations and to reduce the time and skill required therefor;Tand to lower the cost of and simplify the apparatus needed thereby.

In practicing my invention I attain the foregoing and other objects bythe laid of ,a specially constructed instrument of the microscope type.This instrument has the usual objective and eyepiece lenses but issupplemented by -a prism throughwhich light from an external source isintroduced into :the instrument tube. There .this

' ment towards the surface until a second distincl light is directedforwardly past cross hairs in the eyepeces focal plane and projected outof the instrument through the objective lens.

The reflecting surface to be located and meas-.-

ured is placed in the path of these projected light rays where it servesto reflect some of the rays back through the objective into theinstrument tube and thence rearwardly. An observer looks at thesereflected rays through the eyepiece and adjusts the spacing between theinstruments 0bjective and the reflecting surface until a sharplydistinctive appearance of what he sees tells him that 'the objectivesfocal point is exactly coincident with the center of curvature of thesurface being observed. Having so positioned the instrument with respectto that surface, a first distance reading is taken. .I

The observer next brings the instrument ob'- A jectives focal point intocoincidence With the re-*A j' (Granted under the act of March 3, 1883,as f amended April 30, 1928; 370 O. G. 757),Y

fleeting surface its-elf. In the case of a concave surface this is doneby advancing the instrutive appearance of the reflected rays reachingthe eyepiece tells the observer that the condition stated has beenrealized; in the case of a con- Vex surface the same result requiresthat the instrument be backed away. A second distance reading is nowtaken. Subtraction with respect to the first gives the reflectingsurfaces radius of curvature. Illustrative embodiments of my improvedapparatus are shown bythe accompanying drawings wherein:

Fig. 1 isa top plan view partly in section showing one form ofinstrument and mounting by which lmy invention may vbe practiced;

Fig. 2 is a view in side elevation of the same instrument adjusted onthe center of curvature of a concave lens;

Fig. 3 is la section on Fig. ls line 3-3 showi ing the instruments prismand cross hairs as viewed from the rear;

Fig. 4 represents the light halo which develops around the prism undernon-coincident positionings of Ithe instrument;

Figs. 5 and 6 show how coincident lpositioning may be detected in aslightly different manner; A Fig. 7 shows the instrument of Fig. 1adjusted on the surface of the concave lens being measured;

Fig. 8 illustrates certain optical .phenomena believed to accompany thesurface location of Fig. 7

Fig. 9 indicates how the observing instrument is Iable to locate thecenter of a metal sphere;

Fig. 10 shows adjustment of the instrument;

The surface 'observing instrument and mount The surface observinginstrument preferred for the practice of my invention is of a speciallyconstructed microscope type. In the illustrative form which Figs. l-2show this instrument utilizes a hollow tube 20 carrying an objectivelens holder 2| in its forward end and an eyepiece or ocular 22 at itsrear; a .prism 23'extending through .the

that the surface may Ialso be part of a convex' lens as shown at 29 inFig. 1l; -or part of a flat object as shown at 3l) in Figs. 12-13; orpart of a metal sphere as shown at 3| in Figs. 9-10; or part of anyother object (not shown), regardless of material or shape, which iscapable of reflecting light.

The named mount for the observing instrument may be of the vertical"microscope type (not shown) or have the horizontal lens bench formwhich Figs. 1-2 illustrate. There a horizontalbench bar 34 supports anobject holding fixture 35 and an instrument bracket 36 in adjustablyspaced relation with re spect to each other. In the arrangement shownthe fixture 35 is stationary except for a rotative adjustment about basebolt 3l.

The instrument bracket 36, however, is movable along bench bar 34 toward`and away from the object holder 35. Making this movement possible aretop and intermediate bracket bases 39 and 40 which may manually beIpushed along bar 34 to effect approximate positioning adjustments ofinstrument 20, and which also may be moved by Vernier screw 4| withrespect to each other to effect finer adjustments in the instrumentsposition.

A lens bench of this type holds the instruments optical axis parallel tothe bench bar 34 regardless of where it is positioned therealong. Once,therefore, the object 28 to be observed has been squared off, in itssupporting fixture 35, and centered with respect to that axis,v suchrelation is continued even though the instrument be brought closer to orbacked away from the object.

For measuring the distance at which the instrument is so adjusted fromthe object, the bench bar 34 may conveniently be marked with therepresented scale graduations andan extension 42 from the instrumentssupport 39 may carry Vernier markings for registry with the bench barsdistance graduations as illustrated. As the description proceeds it willbe seen that other scale arrangements also are useable.

'The instruments optical elements As illustratively here shown,instrument tube 20 so receives objective lens holder 2| in its forwardend as to permit removal and substitution of other objective holders,and so receives-'eyepiece holder 22 in its rearward end yas to permitinterchange with other Oculars of similar physical dimensions.Optionally, of course, objective and eyepiece elements of satisfactoiyoptical characteristics may be permanently mounted in the tubes twoends.

The objective element in the forward holder 2| has been represented as asimple lens 45. Such representation is intended to typify Objectiveelements having focal length and magnification characteristics of widevariety. In practice highly corrected compound lenses preferably arehere used. One three-lens objective which has satisfactorily been soemployed is shownA by Sabel 4 Patent 1,557,503 (expired), issued October13, 1925.

That illustrative objective has a focal length l of0.25 inch and amagnifying power of 10. As

Athe description proceeds it will be seen that objectives having greateror lesser focal lengths and greater or lesser magnifying powers also areuse- -able for the surface observing purposes here disclosed.

The eyepiece or ocular in the instrument tubes rear holder 22 has beenshown as including an eye lens 46 plus a field lens 41. 'Ihisillustrative ocular is of the Ramsden type in which the two lenses haveequal focal lengths, are separated by a distance of about two thirdsthat length, and have a combined magnifying power of about l0.

Multiplying this ocular power by objective lens 45s magnifying power,also illustratively stated to be 10, gives 100 magnifications as thedescribed instruments total power.

The image to be magnified by the represented ocular l22 is formed infront of field lens 41 and in a plane illustratively shown as beingcoincident with the instruments cross hairs 25. Oculars of other typesand of other magnifying powers are, of course, useable. One requirement,however, which must be met in. all instances is that the oculars focalplane be spaced in front of the field lens 41. by a distance greatenough to accommodate the earlier mentioned prism 23 be 4@ focal plane.

tween that focal planey (see cross hairs 25) and f the lens.

As already stated, the purpose of prism 23 is to bring into theinstrument tube 20 and for-- wardly directtherethrough light from anexternal source hereillustratively shown as an electric. bulb 24. Thisprism has the physical shape shown and is secured in a mating openingthrough the instrument tubes side just back of ocular 22s The materialthereof preferably is optical glass.

The prisms inner end is cut to a angle and coated with silver or otherlight reecting material. Light from source 24 enters the prisrns 45square outer end, strikes the 45 reflecting surface, is thereby directedforwardly through the instruments tube 20, and is by objective lens 45projectedcut vof, thetubes forward end. In.v leaving prism 23- thatlight passes through such portions of. cross hairs 25.y as are in itspath.

Those cross. hairs mayy satisfactorily be arranged as shown by Fig. 3.That arrangement utilizes suspension across tube 20 between attachmentsto a ring 44 snugly tted inside the tube. Other formsof support mayv ofcourse be used..l Mounting. on a glass disc or -retiole is, howevyeiyfound to be unsatisfactory` because of objection-- able reflectingpropertiesof the surfaces of suchv glass.

Preferable. positioningofI these cross hairs 25 ,is'just aheadvof (oreven. in contact with) the,v forward surfaceY of prism 23.l Inconditioning the instrument for operation eyepiece 22 is ad-, justed togive Va sharp imageof the cross hairs. This assures that theeyepiecesfocal plane and the cross hairsy are in fact coincident. Under thiscondition images formed in the plane of the cross hairs are clearlyvisible to the observers eye 50'.

Locatingv centers of curvature the surfaces center of curvature. Thiscondition is shown by each of Figs. 1-2 where the focal point ofobjective lens 45 is designated -as f and the center of curvature oflens 28s concave surface (facing instrument 20) is designated as c.

The lens or other object Whose surface is to be observed is firstsquared off and centered with respect to the optical axis of instrument20. In the case of a concave lens of the type shown at 28 the necessarypositioning of the lens in holder 35 may be aided by removing both theeyepiece 22 and the objective 2l from the instrument. Looking throughtube with the naked eye there will now be seen on the lens surface 28 aspot of light projected thereagainst by prism 23 from source 24.

Centeringis effected by sidewise adjustment" backed away from the lensby a distance esti mated to be greater than that shown in Figs. 1-2 asbeing the sum of the objectives focal length and the surfaces radius ofcurvature r. In looking into the eyepiece the observer now sees thecross hairs and interior of the tube (see Fig. 3) under faint generalillumination.

The instrument is next slowly moved toward the lens. As theobjectivesfocal point f gets close to the surfaces center of curvature c therebegins to appear around the edges of prism 23 intensified illuminationwhich forms a halo of the type shown by Fig. 4. With continued movementof the instrument this halo brightens and becomes most brilliantimmediately before the focal point f' coincides with curvature center c.It then sharply disappears behind the prism just as point f moves intoexact coincidence with point Further movement of the instrument towardssurface 28 causes the halo of Fig. 4 to reappear around the prism. Thisreappearance is again sharp and it reaches maximum brightness upon onlya slight departure from focal point and curvature center coincidence.Continued advancement of the instrument towards the surface decreasesthe halos brightness and soon eliminates it altogether. The observeronce more gets the View of Fig. 3 under very slight generalillumination. i "f-f The halo method of curvature center loca-y f tionjust described is exceedingly accurate,and.

dependable measurements as fine as 0.001fin'ch can in practice reliablybe made. Based on extensive use of the observing instrument over aperiod of months my present analysis of the halos optical phenomena isas follows.

Under the coincident conditions shown by Figs. l-2 each ray of light 52emanating from objective 45 passes through points f and c and strikesthe reflecting surface 28 exactly perpendicular. This producesreflection back into the instrument along the very path taken by the rayin leaving prism 23 and coming out of the objective; hence the doublearrows along rayr path 52. f

The renected image of prism 23 thus is pro- 3576 great. image 54disappears altogether and only as earlier described.

jected vin its entirety back into the prism and so cannot be seenthrough eyepiece 22 in cross hair plane 25. This accords with actualbehavior as earlier described. s

Under slightly separated conditions of points fand c the projected raysfrom objective 45 no longer strike surface 28 at exact 90 angles andhence their return paths into the instrument are suciently divergent toexpand the reflected image of prism 23 and thereby make the outerportions of that reection visible around the prisms physical edges, asshown in Fig. 4. Hence the halo" observations earlier described.

As the separation between points f and c becomes wider a majority of theinstruments pro- -jected rays impinge upon surface 28 at suchsubstantial variance from the perpendicular that very few of them can bereflected back into the instrument. No visible halo is therefore nowpresent and only slight general illumination of cross hair plane 25 canbe seen through the eyepiece. This also accords with actual behavior.Center detection by reflected ima-ge An even more accurate indicationof when the instrument objectives focal point f has been brought intoexact coincidence with surface 28's center of curvature c may be hadunder the conditions which Figs. 5-6 show. There the surface 28 beingobserved has been slightly tilted (full lines) out of the exactlysquared oif position (dotted lines) illustrated by Figs. 1-2.

By reason of this slight tilt the image of prism y 23 which surface 28reflects during coincidence of f and c goes back into the instrumentalong some slightly displaced path which Fig. 5s return ray 52 may beassumed to typify. It now does not reenter the prism (as in Figs. 1-2)but instead appears in cross hair plane 25 as a sharp image 54. In sizeand contour this image exactly duplicates the dimensions and shape ofthat portion of the prism by which light is forwardly directed throughtube 20; under sharply focussed conditions even the cross hairs 25 canbe seen (shown dotted in 54) in the prisms image so reflected. Y

This reflected image method of coincidence detection will in mostinstances be found preferable to halo observation as earlier described.It permits, for example, adjustment of point f upon point c to be madewith even greater accuj racy than before. This is because the iinenessof that adjustment now is measured by the sharpness of reflected image54 (Fig. 6) rather than by the absence of that images distortion(halolof by shifting the surfaces optical center very slightly out ofcoincidence with the observing instruments optical axis. In either casethe needed departure is Very small. Too much displacement must, in fact,be guarded against since same will bring the reflected image completelyout of the eyepieces field of view.

As in the "halo observation method of center of curvature detection,prism 23s reflected image 54 (Fig. 6) becomes distorted and enlarged asobjective focal point f is moved in either direction from exactcoincidence with surface 28s center of curvature c. When departurebecomes too afresh-11s.l

faint;generaiiiluminauon .then isvisible through:

eyepiece 22. i

Having so coincided'lby either method) the instrument objectives focalpoint f with surface.

28's center of curvature c, afirst distance read.-

ing .eis-taken.. In the illustrative setup of Figs. I

1-2csuch. a reading has the value of 2.50 inches.

Record of this. instrument position is4 made for` later use indetermining the value of surface 2llsl radiusof; curvature r.

Location of reflecting surfaces The next. step is -to bring'the.instrument ob-.. jectives-focal point f into coincidence with thereflecting ,surface -28 itself. This condition is.

shown by Fig. 7. Except for having been brought closer. to the surfacebeing observed the instruments adjustmentremains unchanged, andtheobjectiv'e's focal point f thus is spaced from tha.

closer to that surface by exactlythe length of the surfaces radius ofcurvature 7' (see Fig. l). A second distance reading is now' taken. Inthe illustrative setup of Fig. 7 such a reading has the value of 1.00inch.` Subtracting this from the rst reading (Figs. 1-2) of 2.50 inchesgives 1.50 inches as the measured radius of curvature of concave surface28.

The foregoing presupposes accurate location of' objective 45's focalpoint j on surface. 28.. By my inventionsuch accurate'location may bemade.

with relative ease and high reliability. Necesl sary procedure will nowbe described.

"i Starting with the instrument spaced from surbrilliancy'just beforethe focal point coincides with surface 28. It then sharply disappearsbehindprism 23 just as point f moves into exact coincidence with thesurface. The observer's eye l?r then sees only the pattern of Fig. 3.

Further movement of the instrument towards surface 28 causes the halo ofFig. 4 to reappear aroundlthe prisrn.v This reappearance is again sharpand it reaches maximum brightness' upon only a'slight focussing of pointf beneath the surface being located. Continued advancement of theinstrument towards-that surface decreases the halos brightness and sooneliminates it. altogether. The observer once more gets the view of Fig.3 under very slight general illumination.

Bythis halo method it is thus possible tor locate reflecting surfaceswith much higheraccuracies t'han have heretofore been possible.Dependable measurements nner than 0.001 'inch can in practice reliablybe made.

explained for center-of curvature location, and

the observed halos are even more intense and.

hence even more readily discernible- The optical phenomena believed-totake place may bestbe explained by reference to the enlarged diagram ofFig. 8. Under the"coinci dentf,conditons depicted byFigs; 7-8 all rays"Squaring off and centering requirements of the observed sur' face aremuch less critical than those earliery 8": ofrlightzgemanating.fromobjective converge onthe surface y28 at focalpoint f.' Fig. 8 shows atand 56v .two such rays which respectively come.v from the upper andlower-portions of prism l 2'3s .reflecting area.

'Theupper ray 55 strikes surface 28 at such an angle as to reflect backalong the path of lower ray; thatlower ray so strikes the surface as to'reflectback into t'he instrument along the path of' upper.v ray 55; andintermediate rays (not shown). inf both planes behave in such similarAmanner. that the image of prism 23 reflected fromzsurface 28 goes backinto the instrument in; inverted form but otherwise along the paths ofthe. projected rays which produced it.l In con-- sequence the reflectedimage of prism 23 thus is projected in its entirety back into the prismand so cannot 'be seen through eyepiece 22 in cross This accords withactual be hair plane 25. havior as earlier described. Y

Under slight separation (in either direction) of focal point f from thesurface 28, the projected Arays from objective 45 no longer strike thatsurface at the angles necessary t0 set up the conditions shownby Fi'g.8.Their return paths into the instrument now are sufficiently divergent toexpand thev reflected image of prism 23 and thereby make. the outerportions of that reflection .visible aroundtheprisms physical edges, asvshown in Fig. 4. Hence the halo observations earlier described.

Asthe separation.(again in either direction) between .focalpoint f andsurface 28 becomes widerv a'majorityrof thel instruments projected raysimpinge upon. that surface at such substantial angular variance from theFig. 8 condition that very few'of them can be reflected back into the.instrument. No visible halo is ,therefore now present andonly slightgeneral'illumination of ,cross hair plane 25 can be seen through theeyepiece.- This also accords with actual behavior as earlier described.

Reflecting surfaces other than that of con-y cave-contour shown at 28also may be located by my improved "halo method. This method thus isuseablev to locate convex surfaces of the type shown by Figs. l0 and 11at 3l and 29; or fiat.

surface such as. Figs. 12 and 13 show at 30 and 58.

In each of these further instances the procedure duplicates that alreadydescribed, and the optical phenomena also is believed to be the same.Objective 45s focal point f contacts such a small areaof anyobservedsurface that same may be considered fiat. Thus concave,Y convex and flatreflecting surfaces all react the same. Actual use of the halo locatingmethod uponffwide variety of reflecting surface contours bears this outvery convincingly.

Even plain white paper is found to produce. .the-halo. effects underdiscussion. Such paper has been coincided with transparent object 305second surface 58.;

Vcoincidence with point c.

Instrument positioning by halo disappearance is exactly the same as thatdescribed for location of first surfaces. Since, however, theinstruments projected rays pass through object conditions describedcontinue to hold true. 'Ihis may be explained as follows.

Under the coincident conditions shown by AFig. 9 each ray of light 52emanating from ob- 30s glass or other transparent material, the x 51"jective 45 strikes the convex surface 3| exactly spacing from objective45 of Fig. 13s focal pointA a f' can be expected to be somewhatdifferent than the constant value represented for f in the earlierviews.

C'urvature measurement of convex surfaces y It has been seen how concavereflecting surfaces, typified by lens 28 of Figs. 1-2, 5, '7, 8 may havetheir radii of curvature accurately measured by the improved apparatusof my invention.

reflecting surface material, is shown as the ob- 2 ject to be someasured. One requirement to be met here is that the convex surfacesradius of curvature r (Fig. 10) not exceed the spacing of focal point ffrom the instruments objective lens 45. Reason for this requirement isfurther discussed later. As in the case of concave surface measurements,the objectives focal point f is successively coincided with the convexsurfacescenter of curvature c and then with the surface itself; theinstruments position with respect to the convex surface is in each casemeasured in terms4 of spacing distance; and the smaller of these twodistances is subtracted from the larger to give the surfaces radius ofcurvature r.

Bringing of the instrument objectives focal 35 point f into coincidencewith the convex surfaces center of curvature c may best be explained byreference to Fig. 9. There the spherical object 3| is shown as havingbeen squared off and centered with respect to the optical axis ofinstrument 20.

Starting with the instrument spaced from object A3|s surface by adistance estimated to be greater than that shown in Fig. 9, slowmovement toward that surface is then begun. In looking into eyepiece 22the observer first sees the cross hair and prism pattern of Fig. 3 underfaint general illumination.

As the objectives focal point f gets close to the perpendicular. Thisproduces reflection back into the instrument along the very path takenby the ray in Aleaving prism 23 and coming out of the objective; hencethe double arrows along Fig.

10 9s ray path 52. The reflected image of prism 23 thus is projected inits entirety back into the prism and so cannot be seen through eyepiece22.

in cross hair plane 25.

Upon slight departures in either direction from the coincidentconditions of Fig. 9, the projected rays from objective 45 no longerstrike surface 3l at exact 90 angles and hence their return paths intothe instrument are sufficiently i divergent to expand the reflectedimage of prism 0 23 and thereby make the outer portions of that.reflection visible as the Fig. 4 halo around the prisms physical edges.As the departure .be-

comes greater a majority of the instruments projected rays impinge uponsurface 3|at such 25 substantial variance from the perpendicular that-very few of them can now be directed back into the instrument, and thevisible halo therefore disappears. y

The just described halo observation method of curvature center locationrequires that the convex surface 3| under examination be centered andsquared off with respect to the instruments optical axis. Even moreaccurate location of that vsurfaces curvature center c is possible byuse of the alternate reflected image method earlier described (forconcave surfaces) by reference to Figs. 5-6.

To condition the observing setup of Fig. 9 for practice of the lattermethod it is only necessary 40 to shift the sphere 3| slightly to oneside, and

in cross hair plane 25 as an illuminated area represented at 54 in Fig.6. y

In size and contour this image 54 as so reflected from convex surface 3|exactly duplicates the dimensions and shape of that portion of prism urace s center of curvature c there begms to ap 23 by whlch l1ght 1sforwardly directed through pear around the edges of prism 23 intensifiedillumination which forms into the Fig. 4 halo.

' With continued movement of the instrument this halo brightens andbecomes most brilliant immediately before the focal point f coincideswith curvature center c. It then sharply disappears 55 around the prism.This reappearancefisgagain ,Q -faint general illumination then 1svisible through sharp and it reaches maximum brightness upon only aslight departure from focal and curvature point coincidence. Continuedadvancement of the instrument towards surface 3| decreases the halosbrightness and soon eliminates it altogether. The observer once moregets the view of Fig. 3 under very slight general illumination.

The foregoing halo phenomena take place regardless of whether the sphere3| is of transtube 20; under sharply focussed conditions even the crosshairs 25 can be seen (shown dotted within 54 of Fig. 6) in the prismsimage so reflected. 1

eyepiece 22.

Having so coincided (byeither method) the instrument objectives focalpoint f with convex surface 3|s center of curvature c, a rst distancereading of the instruments position (Fig. 9) is taken. Such reading isobtainable from position registering scales (not shown in Fig. 9) of thetype illustrated by Figs. 1-2 and 7. To facilitate exparent materialsuch as glass or of non-transplanation it will be assumed that this Fig`9 parent material such as steel. In either case it is not necessary thatthe objectives focal point f physically penetrate into the spherescenter. Even though (as in the case of a steel sphere) reading has thevalue of 0.50 inch.

The next step is to bring the instrument objectives focal point f intocoincidence with the convex surface 3l itself. This condition is shownno light goes beneath reflecting surface 3|.,the 75 by Fig. l0. Alloperations .incident thereto al- As objective focal point j is moved ineither 'ready having l.been iexplained, the same-will not be repeatedhere. A second distance reading of the instruments .position (Fig. `10)isv now taken.

- Assuming it Yto have the value-of L inch, subtraction therefrom ofvthe first reading (Fig. i9)

of v0.50 inch gives 0.50 inch as the measured radius of curvature r Aofconvex surface 3 l. vSince the complete spheres diameteris equal to 2r,adiam- -eter gure of. 1.00 inch has at the same time been v ascertained.

Quite obviously the complete sphere need :not be available in order topermit .curvature measurement of any section of its surface. As :long

' as the section-under examination is larger-enough lto permit propersupport and alignment with respect .to the observing instrument, radiusofv curvaturez'measurement by the .foregoing method maysatisfactorily'be made.

'Asearlier stated, the instrument .'objecves lfocal .length or workingdistance must ineach 1 instance be greater than the curvature radius 1'of the convex surfaceunder observation. .Reason yfor this `:may be seenfrom Fig. .11. .Surface 29 '.:of that gure has a radius of curvature'rso`much greater.than'thefocalzlength of objective '45 that pointwillfa'll far short of 'reachingpoint c even when thevinstrumentisbrought as close' to surface 29 as is physically possible,

(To reach that `surfaces center will' require u'se -pf aflonger focallength objective such as Fig. 14 ;.shows atl 45. E'Ihat .objectives'focal :point' f" being-more Y.widely spaced from lens145 than is .centerof curvature c fromconvex `surface29, :radius of curvature measurementis possible therewith.

Summary The improvements of my invention are'char- '.acterized yby highutility and broad application. By means of the apparatus here disclosedlight refleeting surfaces identified with a wide variety of shapes,contours and materials may accurately "measured for curvature radius toaccuracies consistently better than 0.001 inch. Best accuracieslattainable with spherometers, steel and `brass radius-gages, and othertest devices of the prior art have varied from 0.005 inch to 0,150 inch.In using my improved technique, moreover', differments to theV 0.001inch accuracy rst stated above.

The same applies to the location of glassv and `other reflectingsurfaces. My lhalo disappearance technique completely eliminates anerror characteristic of prior art surface -locations wherein theoperator has had to judge where the observed surface is by usingscratches into the Asurface and hence beneath the level thereof, or

by using lint and powder on the surface and hence protruding above thelevel thereof.

Another very practical advantage of my invenrtion is that it simpliesand lowers the cost of Asurface locating and curvature radius measuringapparatus. Microscope type observing instruments of my unique design canbe constructed at very moderate cost. When compared With the investmentrepresented by spherometers, metal 4radius gages and other prior artdevices tlis cost .is so low as to make substantial savings possible.

-.i12 ...At the same time the precision of measurement wis increased, asalready noted, and the skill called vfor'on lthe part of operators'isdecreased. This results from the inherently simple construction "of`myAobserving instrument and its mount, and

...from the simplicity -of technique in making observations. Mastery ofthis technique, even by an Iinexperienced operator, is found to requireonly a few hours of instruction and manipulation l0 practice.

Spherometers and other measuring devices of the prior art have, by wayof contrast, required Vmuch :longer periods of `instruction and more.careful supervisionin use. `Even when manipu- ,15 lated with extremeskill, the aecuracies obtainable .by .theseprior art .devicesfall farshort of those desirableiand now-made possible through use of myimproved apparatus and technique.

From the foregoing it will thus be seen that I.. have provided improvedapparatus by which .the location and the curvature of surfaces of glass,metal or other material capable'of reflecting Y .iight may readily bedetermined; that I have .facilitated accurate location of reflectingsurfaces .having-a 4wide variety of shapes and contours including flat,concave and convex; that I have 4`facilitated curvature measurement ofreflecting surfaces having either concave 'or convex coni-tour and beinga part of mirrors, optical lenses,

` metal balls,- sections thereof and-other elements .of variousshapesand materials; and that I have .increased the accuracy andreliabilitywith which v.such location and measurements may be effected, have-simplied the procedure of the named oper 35A ations and reduced thetime and skill required l-ent -observers can repeat each othersmeasureltherefoig and have lowered the cost of and simpli- .-ed theapparatus needed thereby.

.-JMyinventive improvements aretherefore extensive in their adaption andnot to be restricted 40 to the specic form here disclosed by way ofillustration.

I claim:

1. In an instrument for observing a reflecting surface, the combinationof, an instrument 'mount, an instrument tube supported by said -mount,an objective lens carried by the forward end of said tube and having afocal point spaced i externally of said tube from vsaid end, an eyepiececarried by the other end of said tube and having '.a focal plane spacedahead of the eyepiece within the tube, a relatively small prismextending 'fthrough the wall of said tube intermediate said 1:eyepieceand said focal plane and covering only a -small portion of the eld ofview of said eyepiece and serving to transmit into the tube rays offlight from an external source and to projectsame forwardly through thetube and thence outwardly therefrom through said objective lens, meansfor preventing the passage of light through said prism `to saideyepiece, means also supported by said instrument mount for positioninga reflecting surface to be observed in the path of said projected lightrays in such manner that a portion of those rays will be reflected fromthat surface back through said objective lens and into said instrumenttube, the means supporting said tube on said mount being movably mountedlthereon so as to permit relative movement therebetween vin a directionparallel to the axis of the tube for adjusting the spacing between saidobjective'lens said objectives focal point has been brought into fllcoincidence with said surface or with the center of curvature thereof.

2. In an instrument for observing a reflecting surface and locatingsame, the combination of, an

instrument mount, an instrument tube supported by said mount, anobjective lens carried by the forward end of said tube and having afocal point spaced externally of said tube from said end, an eyepiececarried by the other end of said tube and having a focal plane spacedahead of the eyepiece within the tube, a relatively small prismextending through the wall of said tube intermediate said eyepiece andsaid focal plane and covering only a small portion of the field of viewof said eyepiece and serving to bring into the tube rays of light froman external source and to project same forwardly through the Atube andthencebutwardly therefrom through said objective lens, means forpreventing the passage of light through said prism to said eyepiece,means also supported by said instrument mount for positioning areflecting surface to be observed in the path of said projected lightrays in such manner that a portion of those rays will be reflected fromthat surface back through said objective lens and into said instrumenttube, the means supporting said tube on said mount being movably mountedthereon so as to permit relative movement therebetween in a directionparallel to the axis of the tube for adjusting the spacing between saidobjective lens and said surface whereby an observer viewing saidreflected rays through said eyepiece is from a sharply distinctiveappearance thereof in the eyepieces focal plane able to determine l whensaid objectives focal point has been exactly brought into coincidencewith that surface, and

measuring means, a part of which is connected with said mount, forregistering the position of said instrument tube with respect to saidsurface.

3. In an instrument for observing a reflecting surface and locatingsame, the combination of, an instrument mount, an instrument tubesupported by said mount, an objective lens carried by the forward end ofsaid tube and having a focal point spaced externally of said tube fromsaid end, an eyepiece carried by the other end of said tube and having afocal plane spaced ahead of the eyepiece within the tube, a relativelysmall prism extending through the wall of said tube intermediate saideyepiece and said focal plane and covering only a small portion of thefield of view of said eyepiece and serving to bring into the tube raysof light from an external source and to project same forwardly throughthe tube and thence outwardly therefrom through said objective lens,means for preventing the passage of light through said prism to saideyepiece, means also supported by said instrument mount for positioninga reecting surface to be observed in the path of said projected lightrays and with its optical axis vsub- ."coincidence with said surface,

4. In an instrument for observing a reiiecting surface and locating thecenter of curvature thereof, the combination of, an instrument mount, aninstrument tube supported by said mount, an

l0 objective lens carried by the forward end of said tube and having afocal point spaced externally of said tube from said end, an eyepiececarried by the other end of said tube and having a focal plane spacedahead of the eyepiece within the tube, a relatively small prismextending through the wall of said tube intermediate said eyepiece andsaid focal plane and covering only a small portion of the field of viewof said eyepiece and serving to bring into the tube rays of light froman external source and to project same forwardly through the tube andthence outwardly therefrom through said objective lens, means alsosupported A by said instrument mount for positioning a reecting surfaceto be observed in the path of Said projected light rays and with itsoptical axis very slightly displaced from that of said instrument tubewhereby there is reiiected from the surface back through said objectivelens and into the instrument tube an image of said prism which issharply visible through said eyepiece in the said focal plane thereofwhen said'objective lens' focal point is accurately brought intocoincidence with the reflecting surfaces said center of curvature butwhich becomes blurred and indistinct when the named condition ofcoincidence is only slightly departed from in either direction, themeans supporting said tube on said mount being movably mounted thereonso as to permit relative movement therebetween in a direction parallelto 40 the axis of the tube for adjusting the spacing into accuratecoincidence with said reiiecting surfaces center of curvature.

5. In an instrument for determining the radius of curvature of an objecthaving a curved refiecting surface, an optical viewing device comprisinga mounting tube, an objective lens and an ocular lens in and adjacentrespective ends of said tube,

cross hairs mounted within said tube between said lenses andsubstantially in the focal plane of said ocular, means closely adjacentsaid cross hairs to project light forwardly through said objective ontothe spherical reecting surfaee of said object, a holder mounting theobjectf-holder for said viewing device, a bench bar mounting saidholders for relative translation toward and from 50 each other along theoptical axis of said device stantially coincident with that of saidinstrument focal point of said objective lens can be brought tubewhereby there is reflected from the surface back through said objectivelens and into the instrument tube an image of said prism which is by theprism itself blocked from view through said eyepiece when said objectivelens focal point is accurately coincided with said surface but whichexpands as a halo around said prisms edges and hence become visiblethrough the eyepiece when the named condition of coincidence is onlyslightly departed from in either direction, the

means supporting said tube on said mount being movably mounted thereonso as to permit relative movement therebetween in a direction parallelto the axis of the tube for adjusting the spacing into coincidence withsaid reflecting surface or with its center of curvature, and measuringmeans carried by said bar and one of said holders to determine thedistance of said relative translation.

6. In an instrument for determining the radii of curvature of objectshaving spherical reflecting surfaces, a Viewing device comprising atube, an

objective lens and an ocular lens mounted in said tube, each adjacentone end thereof, cross hairs mounted in said tube in the focal plane ofsaid ocular lens, means closely adjacent said cross hairs to projectlight forwardly along the optical axis of said device and through saidobjective 1' 'HERBERT S. EWING.

"The following 'references-are vofI record in the REFERENCES CITED file:of this.' patent:

'UNITEDSTATES PATENTS lNumber l' --N ame :Date ,1,736}682 .,.TuckermanfNov. i9, -1929

